1. Field of the Invention
The present invention relates to a silent chain in which a guide row and a non-guide row adjacent to each other in a longitudinal direction are coupled so as to be bendable by a rocker pin including a long pin and a short pin.
The silent chain is provided in a chain drive system, and the chain drive system is used in, e.g., power equipment for an automobile.
2. Description of the Related Art
Conventionally, in a silent chain having a rocker pin that couples a guide row and a non-guide row such that the guide row and the non-guide row are bendable, the rocker pin includes a long pin and a short pin.
Referring to FIG. 9, in a silent chain 500, a long pin 540 of a rocker pin 504 is held in guide pin holes 513 of a pair of guide plates 511 and 512 so as not to slip out therefrom, and is inserted into first pin holes 523 of a plurality of first plates 520 and second pin holes 533 of a plurality of second plates 530. A short pin 550 of the rocker pin 504 is inserted into the first pin holes 523 and the second pin holes 533.
Incidentally, to the silent chain 500 after its assemble, for the purpose of removing assembly distortion, a proof load as a tensile load set to be larger than tension occurring during travel of the silent chain 500 is normally applied in a longitudinal direction of the chain. In the silent chain 500 in which the tension is generated by the application of the proof load, there are cases where end surfaces 553 and 554 of end portions 551 and 552 of the short pin 550 that is movable in a width direction of the chain relative to the first and second plates 520 and 530 are positioned in adjacent pin holes 533A and 533B as the second pin holes 533 of adjacent plates 531 and 532 as the second plates 530 adjacent to the guide plates 511 and 512.
For example, as shown in FIG. 9, in a case where the end surface 553 is positioned in the adjacent pin hole 533A, due to the small width of a contact area between the short pin 550, the long pin 540, and a wall surface 538 of the adjacent pin hole 533A in the width direction of the chain, a contact pressure between the end portion 551 having the end surface 553, the long pin 540, and the wall surface 538 becomes extremely large in the adjacent pin hole 533A, and excessive stress concentration occurs in a portion P in the vicinity of the end surface 553 in the end portion 551 due to the contact pressure. At this point, due to the excessive stress concentration occurring in the end portion 551, there are cases where a crack that causes a reduction in the strength of the silent chain 500 occurs in the short pin 550.
In addition, there are cases where the similar stress concentration occurs also in the traveling silent chain 500 when the tension thereof is increased.
To cope with this, there is known a technology for implementing a state where the short pin always extends through the adjacent plates in order to increase the width of the contact area between the short pin, the long pin, and the wall surfaces of the pin holes in the width direction of the chain in the pin holes of the adjacent plates adjacent to the pair of guide plates in the width direction of the chain (see, e.g., Japanese Patent Application Publication No. 2000-320619 (paragraphs 0047 to 0059, FIGS. 4 to 13), and Japanese Utility Model Application Publication No. H7-10586 (claims of utility model, FIGS. 1 and 2)).
Incidentally, when consideration is given to the relative movement of the first plate of the guide row, the second plate of the non-guide row, and the short pin in the width direction of the chain, in order to reliably maintain the state where the short pin always extends through the adjacent plates, the length of the short pin tends to be increased. As a result, there have been a problem that the weight of the silent chain is increased and a problem that the size of the silent chain is increased in the width direction of the chain.